Modern cryptography is based on publicly known mathematical algorithms that operate on binary bit sequences and utilitize secret keys. These modern algorythms are used in encryption, hash functions, message authentication codes (MAC) and digital signatures.   The parties interested in secure communication using modern crypto need to possess the necessary keys (public or private).  In a cyber competition, students will most likely get an encrypted message (with some clues) that needs to be decoded.

Modern Cryptography Concepts:

CTF Evalution Steps (advanced)

In a CTF. you will most likely get basic exercises like the following:

  1. basic substitution and XOR
  2. pseudo-random number generators
  3. stream and block ciphers, and their modes of operation
  4. message authentication codes
  5. Diffie-Hellman key exchange
  6. RSA (public-key cryptography)
  1. Convert hex to base64
  2. Fixed XOR
  3. Single-byte XOR cipher
  4. Detect single-character XOR
  5. Implement repeating-key XOR
  6. Break repeating-key XOR
  7. AES in ECB mode
  8. Detect AES in ECB mode
  1. Focus on discovering patterns in the ciphertext to comprehend how encryption transpired.
  2. Unlike hashing, encryption is not a one-way process, so we can reverse it to obtain the plaintext.
  3. Brute force is the last choice during cryptanalysis, since modern ciphers can have extremely large key sizes. While solving these challenges, you should refrain from mindless brute forcing or using automated tools as far as possible.
  4. Instead, it is best to study the cryptosystem as intricately as possible and develop code breaking skills along the way.